1. Field of the Invention
The present invention relates to a liquid lens, and more particularly, to a variable focus liquid lens capable of adjusting a focal length by an electrical signal without mechanical driving by simultaneously allowing focus adjustment using an electrowetting phenomenon and focus adjustment using a fluid pressure of an electromagnetic actuator integrated with the liquid lens.
2. Description of the Prior Art
In general, a lens module of a high-performance digital camera is configured to include an optical lens made of glass and a lens driving unit for driving the optical lens. In the lens module, in order adjust the focus and magnification of the optical lens, positions between several sheets of the optical lens are controlled by using the lens driving unit.
In this manner, in the high-performance digital camera in the related art, since the lens driving unit for adjusting the focus and magnification needs to be installed, the size of the digital camera inevitably increases, and it is difficult to miniaturize the high-performance digital camera.
Recently, a liquid lens capable of adjusting the focus and magnification of the lens without a lens driving unit has been developed. In the liquid lens, a curvature of a liquid droplet is adjusted due to electrowetting phenomenon, so that the focal length can be adjusted. The principle of the electrowetting is described with reference to FIG. 1. As illustrated in FIG. 1, if a conductive liquid droplet 40 having a diameter of 2 mm or less is dropped on an upper surface of an insulating film 14 which is electrically isolated, a spherical droplet is formed as indicated by the solid line in FIG. 1. If a voltage is applied between a first electrode 13 below the insulating film 14 and a second electrode for the electrolytic droplet, the electrowetting phenomenon occurs as indicated by the dotted line in FIG. 1. In other words, a contact angle θ1 between the conductive liquid droplet 40 and the insulating film 13 before the voltage is applied (V=0) and a contact angle θ2 when the voltage is applied satisfy the relationship of θ1>θ2. In this manner, the electrowetting denotes a phenomenon where the contact angle is changed due to the electric field formed by the voltage applied to the conductive liquid droplet 40 between the first and second electrodes 13 and 14. The contact angle is a value uniquely determined by characteristics of a liquid droplet, another liquid or air surrounding the liquid droplet, and a material of the upper surface of the insulating film 13. Herein, the diameter of the conductive liquid droplet 40 is limited to 2 mm or less in order that the liquid is dominated by surface tension rather than the gravitational force.
However, in the liquid lens of which the focal length is adjusted by the electrowetting phenomenon has a limitation in the adjustable range of the focal length. Therefore, there is a problem in that it is difficult to quantitatively adjust the focal length. In order to compensate for the limitation, a liquid lens which quantitatively adjusts the focus with a high speed by using a fluid pressure generated by a separate fluid pressure driving unit installed outside the liquid lens has been developed. However, in the liquid lens, a separate fluid pressure generating unit is needed, so that it is difficult to put the liquid lens to practical use. In addition, there is a problem in that the size of the liquid lens increases due to the fluid pressure generating unit.